Swedish Patent Application 8500530-4 discloses a powder sprayer in which use is made of an elongate, annular charging channel which is inwardly defined by an elongate rod of insulating material and which is outwardly defined by a tubular body of insulating material.
In certain cases, a sprayer of this configuration may function satisfactorily, but it suffers, not least, from the drawback that the powder cloud emitted from the nozzle at the discharge end of the gun shows a tendency to `kick back` onto the external surfaces of the gun so that a considerable amount of powder is deposited there. Furthermore, the charging level will be uneven, and, in certain powder qualities, so low that satisfactory powder coating cannot be achieved.
Swedish Printed Application 446 825 discloses another type of powder sprayer which includes a plurality of irregularly bent charging channels of insulating material through which a powder-air mixture is positively forced for charging the powder. Each one of these irregularly bent charging channels has on its outside an electrically conductive layer.
The construction according to this Printed Application also suffers from considerable drawbacks, partly in that the charging result will not be satisfactory, and partly in that the powder spraygun is constructed in such a manner that it is as good as impossible to clean in conjunction with change of powder quality.
Further problems which are inherent in prior art powder sprayguns reside in the fact that such high tensions have locally been formed in the gun that spark formation or discharges more or less of the light-arc nature have occurred in or at the gun. If such discharges have taken place in contact with the powder in the gun, in certain cases the powder has melted or sintered to form a large aggregate which has caused operational disruptions or a poor end result.